Microstructure Characteristics and Comparative Analysis of Constitutive Models for Flow Stress Prediction of Inconel 718 Alloy

An accurate constitutive model is essential for analyzing deformation behavior of material and reliable numerical simulations in metal forming processes. In this study, hot tensile tests of Inconel 718 alloy have been conducted over a wide range of temperatures (300-973K at an interval of 100K), strains (0.01-0.3 at an interval of 0.01) and quasi-static strain rates (0.0001, 0.001, 0.01s(-1)). Flow stress behavior is significantly affected by test temperatures and strain rates. Microstructure characteristics of deformed test specimens have been examined using scanning electron microscope and electron backscatter diffraction (EBSD). The fractography study revealed that fracture is mix-mode type, i.e., ductile and brittle. Subsequently, EBSD analysis shown that dynamic recrystallization mechanism is more pronounced at a higher temperature. Furthermore, four constitutive models, namely modified Cowper-Symonds, modified Johnson Cook, modified Zerillie-Armstrong and integrated Johnson Cook-Zerillie-Armstrong (JC-ZA) models have been investigated for flow stress prediction. Capability of models has been evaluated based on the correlation coefficient (R), average absolute error (Delta) and its standard deviation (delta). Accurate prediction of flow stress behavior is found by integrated JC-ZA model with R=0.9873, Delta=2.44 and delta=4.08%.